Quote:
Originally Posted by Adrian R
Yo Ken man...
With a 50w you are biasing ONE tube at a time, or ONE side in which equates to one tube. On the hundred watter you are biasing TWO tubes together at one time in which ALSO equates to one side. Measure your plate voltage and do the simple calculation 25w(EL34 tube)\PV x.06 -.07 = bias at idle.
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This part is correct.
Quote:
Originally Posted by Adrian R
Think in common terms man...It is the SUM of all tubes....and cannot exceed the proper bias range...Think of the older Marshalls that had only one bias trim pot...this should help...
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But this is incorrect. If you're measuring off the bias pins in the back, you double the amount because you're reading the tubes as combined pairs. Checking the bias per tube off the socket and then checking off the bias pins will illustrate this. With the older amps with only one bias pot, the idea is that you would measure the bias on each tube individually and then adjust the bias pot so that your hottest tube doesn't exceed your target of 60% - 70%.